Not sure why you would want to specifically do that since you can boot from a normal graphics install and just use the shortcut ctrl+shift+F# to change to the TTY.

However if you really want to just edit you GRUB config and copy paste the the menu entry you want to duplicate, and to one of them add a "space" and the number "3" to the end of the line. This way one entry would boot the graphics mode and the other would boot directly to TTY.

The solution is found here https://www.linux.org/threads/grub-menu-entry-to-boot-to-tty.44508/ and perhaps a thread like this would better fit here !linux4noobs@programming.dev

It might be possible to boot into a bootable image from grub so you don't need to set up another bootable partition.

Or you could disable your display manager in systemd. This will start in console, then if you want X just run startx.

Or you could change your display manager to Lemur, which supports X, Wayland, and TTY sessions.

Or you could just press control-alt-F2 at the login screen to switch to a console.